Regulation of Cell Proliferation and Migration by TAK1 via Transcriptional Control of von Hippel-Lindau Tumor Suppressor
2009; Elsevier BV; Volume: 284; Issue: 27 Linguagem: Inglês
10.1074/jbc.m109.002691
ISSN1083-351X
AutoresSiew Hwey Tan, Mintu Pal, Ming Tan, Marc Hai Liang Wong, Fong U. Tam, Jamie Wei Ting Teo, Han Chung Chong, Chek Kun Tan, Yan Yih Goh, Mark Boon Yang Tang, Peter Cheung, Nguan Soon Tan,
Tópico(s)Diabetic Foot Ulcer Assessment and Management
ResumoSkin maintenance and healing after wounding requires complex epithelial-mesenchymal interactions purportedly mediated by growth factors and cytokines. We show here that, for wound healing, transforming growth factor-β-activated kinase 1 (TAK1) in keratinocytes activates von Hippel-Lindau tumor suppressor expression, which in turn represses the expression of platelet-derived growth factor-B (PDGF-B), integrin β1, and integrin β5 via inhibition of the Sp1-mediated signaling pathway in the keratinocytes. The reduced production of PDGF-B leads to a paracrine-decreased expression of hepatocyte growth factor in the underlying fibroblasts. This TAK1 regulation of the double paracrine PDGF/hepatocyte growth factor signaling can regulate keratinocyte cell proliferation and is required for proper wound healing. Strikingly, TAK1 deficiency enhances cell migration. TAK1-deficient keratinocytes displayed lamellipodia formation with distinct microspike protrusion, associated with an elevated expression of integrins β1 and β5 and sustained activation of cdc42, Rac1, and RhoA. Our findings provide evidence for a novel homeostatic control of keratinocyte proliferation and migration mediated via TAK1 regulation of von Hippel-Lindau tumor suppressor. Dysfunctional regulation of TAK1 may contribute to the pathology of non-healing chronic inflammatory wounds and psoriasis. Skin maintenance and healing after wounding requires complex epithelial-mesenchymal interactions purportedly mediated by growth factors and cytokines. We show here that, for wound healing, transforming growth factor-β-activated kinase 1 (TAK1) in keratinocytes activates von Hippel-Lindau tumor suppressor expression, which in turn represses the expression of platelet-derived growth factor-B (PDGF-B), integrin β1, and integrin β5 via inhibition of the Sp1-mediated signaling pathway in the keratinocytes. The reduced production of PDGF-B leads to a paracrine-decreased expression of hepatocyte growth factor in the underlying fibroblasts. This TAK1 regulation of the double paracrine PDGF/hepatocyte growth factor signaling can regulate keratinocyte cell proliferation and is required for proper wound healing. Strikingly, TAK1 deficiency enhances cell migration. TAK1-deficient keratinocytes displayed lamellipodia formation with distinct microspike protrusion, associated with an elevated expression of integrins β1 and β5 and sustained activation of cdc42, Rac1, and RhoA. Our findings provide evidence for a novel homeostatic control of keratinocyte proliferation and migration mediated via TAK1 regulation of von Hippel-Lindau tumor suppressor. Dysfunctional regulation of TAK1 may contribute to the pathology of non-healing chronic inflammatory wounds and psoriasis. Wound healing is a highly dynamic process that involves complex interactions of extracellular matrix molecules, soluble mediators, various resident cells, and infiltrating leukocyte subtypes. The immediate goal in repair is to achieve tissue integrity and homeostasis. The healing process involves three phases that overlap in time and space, namely inflammation, re-epithelialization, and tissue remodeling. Re-epithelialization is accomplished by increased keratinocyte proliferation and guided migration of the keratinocytes over the granulation tissue. Such processes require ordered changes in keratinocyte behavior and phenotype, which are dictated by the interplay of keratinocytes with dermal fibroblasts, i.e. epithelial-mesenchymal communication. This complex interplay demands the integration of diverse signals through a network of soluble factors exerting autocrine and paracrine activity from the wound microenvironment, culminating in appropriate cellular responses (1.Werner S. Grose R. Physiol. Rev. 2003; 83: 835-870Crossref PubMed Scopus (2541) Google Scholar, 2.Fusenig N.E. Leigh I. Lane B. Watt F. The Keratinocyte Handbook. Cambridge University Press, London1994: 71-94Google Scholar). Aberrations to this signaling network may impair or enhance cell migration and proliferation, leading to insufficient or excessive wound repair and life-threatening consequences such as tumor growth and metastasis. Therefore, to understand the effect of any molecule in normal cellular function, studies into its role in this signaling network and how they culminate to an appropriate cell response become fundamental and necessary.Transforming growth factor-β (TGF-β) 4The abbreviations used are: TGF-βtransforming growth factor-βChIPchromatin immunoprecipitationCK10cytokeratin 10ELISAenzyme-linked immunosorbent assayHGFhepatocyte growth factorHIFαhypoxia-inducible factor αIKKIκB kinaseIL-1interleukin 1JNKc-Jun N-terminal kinasesiRNAsmall interference RNAKCTRLcontrol siRNA keratinocytesKTAK1-BTAK1 siRNA keratinocytesKGFkeratinocyte growth factorMAPKmitogen-activated protein kinaseMEK1MAPK kinase 1MEKK1MAPK kinase kinase 1MKK7MAPK kinase 7OTCorganotypic skin culturePDGFplatelet-derived growth factorPLAproximity ligation assaypVHLvon Hippel-Lindau tumor suppressorqPCRreal-time quantitative PCRSEK1MAPK kinase 4SGKserum and glucocorticoid-inducible kinaseTAK1TGF-β-activated kinase 1TNF-αtumor necrosis factor-αKOknock outcaconstitutively activePBSphosphate-buffered salineTUNELterminal deoxynucleotidyl transferase-mediated dUTP nick end labelingERKextracellular signal-regulated kinaseGSTglutathione S-transferase. 4The abbreviations used are: TGF-βtransforming growth factor-βChIPchromatin immunoprecipitationCK10cytokeratin 10ELISAenzyme-linked immunosorbent assayHGFhepatocyte growth factorHIFαhypoxia-inducible factor αIKKIκB kinaseIL-1interleukin 1JNKc-Jun N-terminal kinasesiRNAsmall interference RNAKCTRLcontrol siRNA keratinocytesKTAK1-BTAK1 siRNA keratinocytesKGFkeratinocyte growth factorMAPKmitogen-activated protein kinaseMEK1MAPK kinase 1MEKK1MAPK kinase kinase 1MKK7MAPK kinase 7OTCorganotypic skin culturePDGFplatelet-derived growth factorPLAproximity ligation assaypVHLvon Hippel-Lindau tumor suppressorqPCRreal-time quantitative PCRSEK1MAPK kinase 4SGKserum and glucocorticoid-inducible kinaseTAK1TGF-β-activated kinase 1TNF-αtumor necrosis factor-αKOknock outcaconstitutively activePBSphosphate-buffered salineTUNELterminal deoxynucleotidyl transferase-mediated dUTP nick end labelingERKextracellular signal-regulated kinaseGSTglutathione S-transferase.-activated kinase 1 (TAK1) belongs to the MAPK kinase kinase family. This serine/threonine kinase is a key intermediate in inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin 1 (IL-1) (3.Ninomiya-Tsuji J. Kishimoto K. Hiyama A. Inoue J. Cao Z. Matsumoto K. Nature. 1999; 398: 252-256Crossref PubMed Scopus (1010) Google Scholar, 4.Sato S. Sanjo H. Takeda K. Ninomiya-Tsuji J. Yamamoto M. Kawai T. Matsumoto K. Takeuchi O. Akira S. Nat. Immunol. 2005; 6: 1087-1095Crossref PubMed Scopus (740) Google Scholar) as well as TGF-β (5.Yamaguchi K. Shirakabe K. Shibuya H. Irie K. Oishi I. Ueno N. Taniguchi T. Nishida E. Matsumoto K. Science. 1995; 270: 2008-2011Crossref PubMed Scopus (1169) Google Scholar)-mediated signaling pathways. Activated TAK1 has the capacity to stimulate its downstream MAPK and NFκB-inducing kinase-IκB kinase cascades (6.Wang C. Deng L. Hong M. Akkaraju G.R. Inoue J. Chen Z.J. Nature. 2001; 412: 346-351Crossref PubMed Scopus (1612) Google Scholar). The former activates c-Jun N-terminal kinase (JNK) and p38 MAPK while the latter activates NF-κB (3.Ninomiya-Tsuji J. Kishimoto K. Hiyama A. Inoue J. Cao Z. Matsumoto K. Nature. 1999; 398: 252-256Crossref PubMed Scopus (1010) Google Scholar, 7.Takaesu G. Surabhi R.M. Park K.J. Ninomiya-Tsuji J. Matsumoto K. Gaynor R.B. J. Mol. Biol. 2003; 326: 105-115Crossref PubMed Scopus (315) Google Scholar, 8.Yao J. Kim T.W. Qin J. Jiang Z. Qian Y. Xiao H. Lu Y. Qian W. Gulen M.F. Sizemore N. DiDonato J. Sato S. Akira S. Su B. Li X. J. Biol. Chem. 2007; 282: 6075-6089Abstract Full Text Full Text PDF PubMed Scopus (94) Google Scholar). A deficiency in TAK1 results in impaired TNF-α- and IL-1-stimulated JNK activity, p38 phosphorylation, and IκBα degradation (7.Takaesu G. Surabhi R.M. Park K.J. Ninomiya-Tsuji J. Matsumoto K. Gaynor R.B. J. Mol. Biol. 2003; 326: 105-115Crossref PubMed Scopus (315) Google Scholar, 9.Shim J.H. Xiao C. Paschal A.E. Bailey S.T. Rao P. Hayden M.S. Lee K.Y. Bussey C. Steckel M. Tanaka N. Yamada G. Akira S. Matsumoto K. Ghosh S. Genes Dev. 2005; 19: 2668-2681Crossref PubMed Scopus (582) Google Scholar). Studies of keratinocyte-specific TAK1 knock-out (TAK1-KO) mice confirmed the role of TAK1 in skin inflammation. These TAK1-KO mice died by postnatal day 7 and developed intra-epidermal micro-abscesses (10.Omori E. Matsumoto K. Sanjo H. Sato S. Akira S. Smart R.C. Ninomiya-Tsuji J. J. Biol. Chem. 2006; 281: 19610-19617Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar, 11.Sayama K. Hanakawa Y. Nagai H. Shirakata Y. Dai X. Hirakawa S. Tokumaru S. Tohyama M. Yang L. Sato S. Shizuo A. Hashimoto K. J. Biol. Chem. 2006; 281: 22013-22020Abstract Full Text Full Text PDF PubMed Scopus (49) Google Scholar). The TAK1-KO mice displayed abnormal epidermis with impaired differentiation and increased cellular proliferation; however, no significant difference in proliferation index was observed in culture of these mutant keratinocytes in vitro. Nevertheless, the latter suggests a crucial role of the underlying dermis in mitigating some effects of epidermal TAK1. Although the role of TAK1 in inflammatory response is well established, the role of TAK1 and its mechanism of action in keratinocyte proliferation and migration remain unknown.Herein, we show that the deficiency in TAK1 resulted in increased cell proliferation and migration. We provide evidence of a double paracrine mechanism that make a pivotal contribution to the enhanced cell proliferation in TAK1-deficient epidermis. This study also reveals a novel homeostatic role of TAK1 in controlling cell migration. These aberrant phenotypes, as a consequence of TAK1 deficiency, are mediated via the dysregulated expression of von Hippel-Lindau tumor suppressor.DiscussionFollowing injury, the restoration of its functional integrity is of utmost importance to the survival of the organism. The regeneration and maintenance of epithelium to close the wound is dictated by epithelial-mesenchymal interactions and purportedly mediated by the action of central players, such as chemokines and growth factors. This communication is crucial for preventing either insufficient or excess wound repair. Previous work has shown that mice with a keratinocyte-specific deletion of TAK1 exhibit severe skin inflammation and display abnormal epidermis with impaired differentiation, increased cell proliferation, and apoptosis (10.Omori E. Matsumoto K. Sanjo H. Sato S. Akira S. Smart R.C. Ninomiya-Tsuji J. J. Biol. Chem. 2006; 281: 19610-19617Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar, 11.Sayama K. Hanakawa Y. Nagai H. Shirakata Y. Dai X. Hirakawa S. Tokumaru S. Tohyama M. Yang L. Sato S. Shizuo A. Hashimoto K. J. Biol. Chem. 2006; 281: 22013-22020Abstract Full Text Full Text PDF PubMed Scopus (49) Google Scholar). In this study, we reveal that keratinocyte-specific TAK1 regulates epidermal proliferation via a double paracrine mechanism and characterize a novel unsuspected role of TAK1 in cell migration. We show that pVHL, whose expression is up-regulated by TAK1/IKK/NF-κB signaling, interacts and sequesters transcription factor Sp1, which is necessary for PDGF-B and integrins β1 and β5 expression.The formation of normal epidermal tissue requires a continuous exchange of signals with the underlying dermal fibroblasts (15.Chong H.C. Tan M.J. Philippe V. Tan S.H. Tan C.K. Ku C.W. Goh Y.Y. Wahli W. Michalik L. Tan N.S. J. Cell Biol. 2009; 184: 817-831Crossref PubMed Scopus (80) Google Scholar, 28.Cheng N. Bhowmick N.A. Chytil A. Gorksa A.E. Brown K.A. Muraoka R. Arteaga C.L. Neilson E.G. Hayward S.W. Moses H.L. Oncogene. 2005; 24: 5053-5068Crossref PubMed Scopus (223) Google Scholar). Keratinocyte-specific TAK1-knock-out mice displayed enhanced epidermal proliferation, which was not observed in monolayer culture, suggesting that dermal fibroblasts have pivotal contribution. We reveal a double paracrine PDGF/HGF signaling that plays an important role in TAK1-mediated epidermal proliferation. For any cells to respond productively to PDGF, they must possess corresponding cell surface receptors, either the α-PDGF or β-PDGF receptors. Although keratinocytes contribute to PDGF activity by their ample capacity to secreted PDGF, they do not express any transmembrane receptor recognizing any classic PDGF isoforms; thus target cells for these ligands in skin are restricted to cells of mesenchymal origin, e.g. dermal fibroblasts (29.Reuterdahl C. Sundberg C. Rubin K. Funa K. Gerdin B. J. Clin. Invest. 1993; 91: 2065-2075Crossref PubMed Scopus (100) Google Scholar, 30.Ansel J.C. Tiesman J.P. Olerud J.E. Krueger J.G. Krane J.F. Tara D.C. Shipley G.D. Gilbertson D. Usui M.L. Hart C.E. J. Clin. Invest. 1993; 92: 671-678Crossref PubMed Scopus (124) Google Scholar). We further show that NF-κB, a downstream mediator of TAK1, regulates the expression of pVHL. The pVHL protein interacts and sequesters transcription factor Sp1, which is required for PDGF-B expression (21.Rafty L.A. Khachigian L.M. J. Cell. Biochem. 2002; 85: 490-495Crossref PubMed Scopus (17) Google Scholar). A similar mechanism was also exploited by pVHL to repress VEGF gene expression (31.Mukhopadhyay D. Knebelmann B. Cohen H.T. Ananth S. Sukhatme V.P. Mol. Cell. Biol. 1997; 17: 5629-5639Crossref PubMed Scopus (304) Google Scholar). PDGF-B was previously reported to increase HGF production in the fibroblasts to stimulate keratinocyte proliferation (32.Lederle W. Stark H.J. Skobe M. Fusenig N.E. Mueller M.M. Am. J. Pathol. 2006; 169: 1767-1783Abstract Full Text Full Text PDF PubMed Scopus (51) Google Scholar). Indeed, PDGF-BB secreted by keratinocytes acts as a paracrine factor to induce HGF production by fibroblasts, which in return, enhance epidermal proliferation (Fig. 6). This study underscores the fact that TAK1 in the epidermal keratinocytes fulfils a homeostatic role during epidermal formation, modulating cell proliferation via a double paracrine fashion, involving the underlying dermal fibroblasts. The paracrine mechanism described herein emphasizes the importance of epithelial-mesenchymal communication in the regulation of epidermal proliferation, which was not observed in TAK1-knock-out monolayer culture.Cell migration during re-epithelialization is equally crucial for efficient wound closure. In this study, we reveal a novel homeostatic role of TAK1 in the control of keratinocyte migration. TAK1-deficient keratinocytes migrate faster, associated with enhanced integrin β1 and β5 expression, activation of FAK, and small Rho GTPases when compared with its wild-type counterpart. The elevated active Rho GTPases expression profile supports a faster migration rate and persistent lamellipodia formation. The functions of pVHL can be mediated via HIFα-dependent or -independent mechanisms. Our findings suggested that hypoxia retarded keratinocyte migration. However, hypoxia-mediated migration is complex and context-dependent. It can be modulated by extracellular matrix, matricellular proteins, matrix metalloproteinases, and other signaling pathways (33.O'Toole E.A. van Koningsveld R. Chen M. Woodley D.T. J. Cell. Physiol. 2008; 214: 47-55Crossref PubMed Scopus (32) Google Scholar). It can also differ among keratinocytes isolated from donors of different age (34.Xia Y.P. Zhao Y. Tyrone J.W. Chen A. Mustoe T.A. J. Invest. Dermatol. 2001; 116: 50-56Abstract Full Text Full Text PDF PubMed Scopus (79) Google Scholar). However, our findings suggest that the mechanism underlying the phenotype of TAK1-deficient keratinocytes is HIFα-independent. Interestingly, TAK1 employs similar regulatory mechanism, i.e. via pVHL to modulate integrin β1 and β5 expression. In support of a role in cell migration for pVHL, it was reported that highly aggressive breast cancer expressed either no pVHL or low pVHL level (35.Zia M.K. Rmali K.A. Watkins G. Mansel R.E. Jiang W.G. Int. J. Mol. Med. 2007; 20: 605-611PubMed Google Scholar). High pVHL expression also resulted in a decrease of tubulin turnover indicating a role for pVHL in cellular processes such as migration, polarization, and cell-cell interactions (36.Lolkema M.P. Mehra N. Jorna A.S. van Beest M. Giles R.H. Voest E.E. Exp. Cell Res. 2004; 301: 139-146Crossref PubMed Scopus (47) Google Scholar).The development, maintenance, and regeneration of the epidermal integrity are likely to involve the concerted effort of numerous signaling pathways, including epithelial-mesenchymal communications. One of such communications is the IL-1/keratinocyte growth factor/granulocyte macrophage-colony stimulating factor double paracrine mechanism (37.Maas-Szabowski N. Shimotoyodome A. Fusenig N.E. J. Cell Sci. 1999; 112: 1843-1853Crossref PubMed Google Scholar). Given the pivotal role of TAK1 in propagating the effect of numerous inflammatory cytokines, such as TNF-α, the PDGF/HGF mechanism described herein complements the IL-1/keratinocyte growth factor/granulocyte macrophage-colony stimulating factor mechanism, particularly during wound repair. TAK1 may also modulate cell migration indirectly via HGF in vivo, when epithelia-mesenchymal interaction is evident. It was recently shown that HGF-mediated cell migration involves a PAK-LIMK pathway (38.Ahmed T. Shea K. Masters J.R. Jones G.E. Wells C.M. Cell Signal. 2008; 20: 1320-1328Crossref PubMed Scopus (106) Google Scholar). It is conceivable that both mechanisms are utilized for epidermal regeneration during wound healing.Psoriasis is a non-contagious chronic inflammatory skin disease characterized by hyperproliferative epidermal growth, a phenotype that was similarly observed in mice with a keratinocyte-specific deletion of TAK1 (10.Omori E. Matsumoto K. Sanjo H. Sato S. Akira S. Smart R.C. Ninomiya-Tsuji J. J. Biol. Chem. 2006; 281: 19610-19617Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar, 11.Sayama K. Hanakawa Y. Nagai H. Shirakata Y. Dai X. Hirakawa S. Tokumaru S. Tohyama M. Yang L. Sato S. Shizuo A. Hashimoto K. J. Biol. Chem. 2006; 281: 22013-22020Abstract Full Text Full Text PDF PubMed Scopus (49) Google Scholar). A recent report suggests that TAK1 deletion causes dysregulation of reactive oxygen species in keratinocytes, which is causally associated with skin inflammation (39.Omori E. Morioka S. Matsumoto K. Ninomiya-Tsuji J. J. Biol. Chem. 2008; 283: 26161-26168Abstract Full Text Full Text PDF PubMed Scopus (78) Google Scholar). Reactive oxygen species has been associated with psoriasis (40.Trouba K.J. Hamadeh H.K. Amin R.P. Germolec D.R. Antioxid. Redox. Signal. 2002; 4: 665-673Crossref PubMed Scopus (215) Google Scholar, 41.Young C.N. Koepke J.I. Terlecky L.J. Borkin M.S. Boyd S.L. Terlecky S.R. J. Invest. Dermatol. 2008; 128: 2606-2614Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar). Our study reveals the underlying mechanism by which TAK1 regulates epidermal proliferation via a double paracrine mechanism involving the underlying dermal fibroblasts. We showed that TAK1 in the keratinocytes directly up-regulated the expression of pVHL, reduced PDGF-B expression, and consequently diminished HGF/c-Met signaling. A deficiency in TAK1 resulted in reduced NF-κB activation and pVHL expression. Lending support, analysis of skin biopsies of patients with psoriasis showed that pVHL, a direct target of TAK1, is underexpressed in psoriatic skin and highly expressed in healthy skin (42.Tovar-Castillo L.E. Cancino-Díaz J.C. García-Vázquez F. Cancino-Gómez F.G. León-Dorantes G. Blancas-González F. Jiménez-Zamudio L. García-Latorre E. Cancino-Díaz M.E. Int. J. Dermatol. 2007; 46: 239-246Crossref PubMed Scopus (83) Google Scholar). Furthermore, PDGF receptor expression was greatly elevated in psoriatic fibroblasts, rendering them highly responsive to PDGF and PDGF-induced HGF production (27.Krueger J.G. Krane J.F. Carter D.M. Gottlieb A.B. J. Invest. Dermatol. 1990; 94: 135S-140SAbstract Full Text PDF PubMed Scopus (203) Google Scholar). Altogether, our findings herein and those of others suggest that TAK1 deficiency may contribute to the etiology of psoriasis. Wound healing is a highly dynamic process that involves complex interactions of extracellular matrix molecules, soluble mediators, various resident cells, and infiltrating leukocyte subtypes. The immediate goal in repair is to achieve tissue integrity and homeostasis. The healing process involves three phases that overlap in time and space, namely inflammation, re-epithelialization, and tissue remodeling. Re-epithelialization is accomplished by increased keratinocyte proliferation and guided migration of the keratinocytes over the granulation tissue. Such processes require ordered changes in keratinocyte behavior and phenotype, which are dictated by the interplay of keratinocytes with dermal fibroblasts, i.e. epithelial-mesenchymal communication. This complex interplay demands the integration of diverse signals through a network of soluble factors exerting autocrine and paracrine activity from the wound microenvironment, culminating in appropriate cellular responses (1.Werner S. Grose R. Physiol. Rev. 2003; 83: 835-870Crossref PubMed Scopus (2541) Google Scholar, 2.Fusenig N.E. Leigh I. Lane B. Watt F. The Keratinocyte Handbook. Cambridge University Press, London1994: 71-94Google Scholar). Aberrations to this signaling network may impair or enhance cell migration and proliferation, leading to insufficient or excessive wound repair and life-threatening consequences such as tumor growth and metastasis. Therefore, to understand the effect of any molecule in normal cellular function, studies into its role in this signaling network and how they culminate to an appropriate cell response become fundamental and necessary. Transforming growth factor-β (TGF-β) 4The abbreviations used are: TGF-βtransforming growth factor-βChIPchromatin immunoprecipitationCK10cytokeratin 10ELISAenzyme-linked immunosorbent assayHGFhepatocyte growth factorHIFαhypoxia-inducible factor αIKKIκB kinaseIL-1interleukin 1JNKc-Jun N-terminal kinasesiRNAsmall interference RNAKCTRLcontrol siRNA keratinocytesKTAK1-BTAK1 siRNA keratinocytesKGFkeratinocyte growth factorMAPKmitogen-activated protein kinaseMEK1MAPK kinase 1MEKK1MAPK kinase kinase 1MKK7MAPK kinase 7OTCorganotypic skin culturePDGFplatelet-derived growth factorPLAproximity ligation assaypVHLvon Hippel-Lindau tumor suppressorqPCRreal-time quantitative PCRSEK1MAPK kinase 4SGKserum and glucocorticoid-inducible kinaseTAK1TGF-β-activated kinase 1TNF-αtumor necrosis factor-αKOknock outcaconstitutively activePBSphosphate-buffered salineTUNELterminal deoxynucleotidyl transferase-mediated dUTP nick end labelingERKextracellular signal-regulated kinaseGSTglutathione S-transferase. 4The abbreviations used are: TGF-βtransforming growth factor-βChIPchromatin immunoprecipitationCK10cytokeratin 10ELISAenzyme-linked immunosorbent assayHGFhepatocyte growth factorHIFαhypoxia-inducible factor αIKKIκB kinaseIL-1interleukin 1JNKc-Jun N-terminal kinasesiRNAsmall interference RNAKCTRLcontrol siRNA keratinocytesKTAK1-BTAK1 siRNA keratinocytesKGFkeratinocyte growth factorMAPKmitogen-activated protein kinaseMEK1MAPK kinase 1MEKK1MAPK kinase kinase 1MKK7MAPK kinase 7OTCorganotypic skin culturePDGFplatelet-derived growth factorPLAproximity ligation assaypVHLvon Hippel-Lindau tumor suppressorqPCRreal-time quantitative PCRSEK1MAPK kinase 4SGKserum and glucocorticoid-inducible kinaseTAK1TGF-β-activated kinase 1TNF-αtumor necrosis factor-αKOknock outcaconstitutively activePBSphosphate-buffered salineTUNELterminal deoxynucleotidyl transferase-mediated dUTP nick end labelingERKextracellular signal-regulated kinaseGSTglutathione S-transferase.-activated kinase 1 (TAK1) belongs to the MAPK kinase kinase family. This serine/threonine kinase is a key intermediate in inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin 1 (IL-1) (3.Ninomiya-Tsuji J. Kishimoto K. Hiyama A. Inoue J. Cao Z. Matsumoto K. Nature. 1999; 398: 252-256Crossref PubMed Scopus (1010) Google Scholar, 4.Sato S. Sanjo H. Takeda K. Ninomiya-Tsuji J. Yamamoto M. Kawai T. Matsumoto K. Takeuchi O. Akira S. Nat. Immunol. 2005; 6: 1087-1095Crossref PubMed Scopus (740) Google Scholar) as well as TGF-β (5.Yamaguchi K. Shirakabe K. Shibuya H. Irie K. Oishi I. Ueno N. Taniguchi T. Nishida E. Matsumoto K. Science. 1995; 270: 2008-2011Crossref PubMed Scopus (1169) Google Scholar)-mediated signaling pathways. Activated TAK1 has the capacity to stimulate its downstream MAPK and NFκB-inducing kinase-IκB kinase cascades (6.Wang C. Deng L. Hong M. Akkaraju G.R. Inoue J. Chen Z.J. Nature. 2001; 412: 346-351Crossref PubMed Scopus (1612) Google Scholar). The former activates c-Jun N-terminal kinase (JNK) and p38 MAPK while the latter activates NF-κB (3.Ninomiya-Tsuji J. Kishimoto K. Hiyama A. Inoue J. Cao Z. Matsumoto K. Nature. 1999; 398: 252-256Crossref PubMed Scopus (1010) Google Scholar, 7.Takaesu G. Surabhi R.M. Park K.J. Ninomiya-Tsuji J. Matsumoto K. Gaynor R.B. J. Mol. Biol. 2003; 326: 105-115Crossref PubMed Scopus (315) Google Scholar, 8.Yao J. Kim T.W. Qin J. Jiang Z. Qian Y. Xiao H. Lu Y. Qian W. Gulen M.F. Sizemore N. DiDonato J. Sato S. Akira S. Su B. Li X. J. Biol. Chem. 2007; 282: 6075-6089Abstract Full Text Full Text PDF PubMed Scopus (94) Google Scholar). A deficiency in TAK1 results in impaired TNF-α- and IL-1-stimulated JNK activity, p38 phosphorylation, and IκBα degradation (7.Takaesu G. Surabhi R.M. Park K.J. Ninomiya-Tsuji J. Matsumoto K. Gaynor R.B. J. Mol. Biol. 2003; 326: 105-115Crossref PubMed Scopus (315) Google Scholar, 9.Shim J.H. Xiao C. Paschal A.E. Bailey S.T. Rao P. Hayden M.S. Lee K.Y. Bussey C. Steckel M. Tanaka N. Yamada G. Akira S. Matsumoto K. Ghosh S. Genes Dev. 2005; 19: 2668-2681Crossref PubMed Scopus (582) Google Scholar). Studies of keratinocyte-specific TAK1 knock-out (TAK1-KO) mice confirmed the role of TAK1 in skin inflammation. These TAK1-KO mice died by postnatal day 7 and developed intra-epidermal micro-abscesses (10.Omori E. Matsumoto K. Sanjo H. Sato S. Akira S. Smart R.C. Ninomiya-Tsuji J. J. Biol. Chem. 2006; 281: 19610-19617Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar, 11.Sayama K. Hanakawa Y. Nagai H. Shirakata Y. Dai X. Hirakawa S. Tokumaru S. Tohyama M. Yang L. Sato S. Shizuo A. Hashimoto K. J. Biol. Chem. 2006; 281: 22013-22020Abstract Full Text Full Text PDF PubMed Scopus (49) Google Scholar). The TAK1-KO mice displayed abnormal epidermis with impaired differentiation and increased cellular proliferation; however, no significant difference in proliferation index was observed in culture of these mutant keratinocytes in vitro. Nevertheless, the latter suggests a crucial role of the underlying dermis in mitigating some effects of epidermal TAK1. Although the role of TAK1 in inflammatory response is well established, the role of TAK1 and its mechanism of action in keratinocyte proliferation and migration remain unknown. transforming growth factor-β chromatin immunoprecipitation cytokeratin 10 enzyme-linked immunosorbent assay hepatocyte growth factor hypoxia-inducible factor α IκB kinase interleukin 1 c-Jun N-terminal kinase small interference RNA control siRNA keratinocytes TAK1 siRNA keratinocytes keratinocyte growth factor mitogen-activated protein kinase MAPK kinase 1 MAPK kinase kinase 1 MAPK kinase 7 organotypic skin culture platelet-derived growth factor proximity ligation assay von Hippel-Lindau tumor suppressor real-time quantitative PCR MAPK kinase 4 serum and glucocorticoid-inducible kinase TGF-β-activated kinase 1 tumor necrosis factor-α knock out constitutively active phosphate-buffered saline terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling extracellular signal-regulated kinase glutathione S-transferase. transforming growth factor-β chromatin immunoprecipitation cytokeratin 10 enzyme-linked immunosorbent assay hepatocyte growth factor hypoxia-inducible factor α IκB kinase interleukin 1 c-Jun N-terminal kinase small interference RNA control siRNA keratinocytes TAK1 siRNA keratinocytes keratinocyte growth factor mitogen-activated protein kinase MAPK kinase 1 MAPK kinase kinase 1 MAPK kinase 7 organotypic skin culture platelet-derived growth factor proximity ligation assay von Hippel-Lindau tumor suppressor real-time quantitative PCR MAPK kinase 4 serum and glucocorticoid-inducible kinase TGF-β-activated kinase 1 tumor necrosis factor-α knock out constitutively active phosphate-buffered saline terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling extracellular signal-regulated kinase glutathione S-transferase. Herein, we show that the deficiency in TAK1 resulted in increased cell proliferation and migration. We provide evidence of a double paracrine mechanism that make a pivotal contribution to the enhanced cell proliferation in TAK1-deficient epidermis. This study also reveals a novel homeostatic role of TAK1 in controlling cell migration. These aberrant phenotypes, as a consequence of TAK1 deficiency, are mediated via the dysregulated expression of von Hippel-Lindau tumor suppressor. DiscussionFollowing injury, the restoration of its functional integrity is of utmost importance to the survival of the organism. The regeneration and maintenance of epithelium to close the wound is dictated by epithelial-mesenchymal interactions and purportedly mediated by the action of central players, such as chemokines and growth factors. This communication is crucial for preventing either insufficient or excess wound repair. Previous work has shown that mice with a keratinocyte-specific deletion of TAK1 exhibit severe skin inflammation and display abnormal epidermis with impaired differentiation, increased cell proliferation, and apoptosis (10.Omori E. Matsumoto K. Sanjo H. Sato S. Akira S. Smart R.C. Ninomiya-Tsuji J. J. Biol. Chem. 2006; 281: 19610-19617Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar, 11.Sayama K. Hanakawa Y. Nagai H. Shirakata Y. Dai X. Hirakawa S. Tokumaru S. Tohyama M. Yang L. Sato S. Shizuo A. Hashimoto K. J. Biol. Chem. 2006; 281: 22013-22020Abstract Full Text Full Text PDF PubMed Scopus (49) Google Scholar). In this study, we reveal that keratinocyte-specific TAK1 regulates epidermal proliferation via a double paracrine mechanism and characterize a novel unsuspected role of TAK1 in cell migration. We show that pVHL, whose expression is up-regulated by TAK1/IKK/NF-κB signaling, interacts and sequesters transcription factor Sp1, which is necessary for PDGF-B and integrins β1 and β5 expression.The formation of normal epidermal tissue requires a continuous exchange of signals with the underlying dermal fibroblasts (15.Chong H.C. Tan M.J. Philippe V. Tan S.H. Tan C.K. Ku C.W. Goh Y.Y. Wahli W. Michalik L. Tan N.S. J. Cell Biol. 2009; 184: 817-831Crossref PubMed Scopus (80) Google Scholar, 28.Cheng N. Bhowmick N.A. Chytil A. Gorksa A.E. Brown K.A. Muraoka R. Arteaga C.L. Neilson E.G. Hayward S.W. Moses H.L. Oncogene. 2005; 24: 5053-5068Crossref PubMed Scopus (223) Google Scholar). Keratinocyte-specific TAK1-knock-out mice displayed enhanced epidermal proliferation, which was not observed in monolayer culture, suggesting that dermal fibroblasts have pivotal contribution. We reveal a double paracrine PDGF/HGF signaling that plays an important role in TAK1-mediated epidermal proliferation. For any cells to respond productively to PDGF, they must possess corresponding cell surface receptors, either the α-PDGF or β-PDGF receptors. Although keratinocytes contribute to PDGF activity by their ample capacity to secreted PDGF, they do not express any transmembrane receptor recognizing any classic PDGF isoforms; thus target cells for these ligands in skin are restricted to cells of mesenchymal origin, e.g. dermal fibroblasts (29.Reuterdahl C. Sundberg C. Rubin K. Funa K. Gerdin B. J. Clin. Invest. 1993; 91: 2065-2075Crossref PubMed Scopus (100) Google Scholar, 30.Ansel J.C. Tiesman J.P. Olerud J.E. Krueger J.G. Krane J.F. Tara D.C. Shipley G.D. Gilbertson D. Usui M.L. Hart C.E. J. Clin. Invest. 1993; 92: 671-678Crossref PubMed Scopus (124) Google Scholar). We further show that NF-κB, a downstream mediator of TAK1, regulates the expression of pVHL. The pVHL protein interacts and sequesters transcription factor Sp1, which is required for PDGF-B expression (21.Rafty L.A. Khachigian L.M. J. Cell. Biochem. 2002; 85: 490-495Crossref PubMed Scopus (17) Google Scholar). A similar mechanism was also exploited by pVHL to repress VEGF gene expression (31.Mukhopadhyay D. Knebelmann B. Cohen H.T. Ananth S. Sukhatme V.P. Mol. Cell. Biol. 1997; 17: 5629-5639Crossref PubMed Scopus (304) Google Scholar). PDGF-B was previously reported to increase HGF production in the fibroblasts to stimulate keratinocyte proliferation (32.Lederle W. Stark H.J. Skobe M. Fusenig N.E. Mueller M.M. Am. J. Pathol. 2006; 169: 1767-1783Abstract Full Text Full Text PDF PubMed Scopus (51) Google Scholar). Indeed, PDGF-BB secreted by keratinocytes acts as a paracrine factor to induce HGF production by fibroblasts, which in return, enhance epidermal proliferation (Fig. 6). This study underscores the fact that TAK1 in the epidermal keratinocytes fulfils a homeostatic role during epidermal formation, modulating cell proliferation via a double paracrine fashion, involving the underlying dermal fibroblasts. The paracrine mechanism described herein emphasizes the importance of epithelial-mesenchymal communication in the regulation of epidermal proliferation, which was not observed in TAK1-knock-out monolayer culture.Cell migration during re-epithelialization is equally crucial for efficient wound closure. In this study, we reveal a novel homeostatic role of TAK1 in the control of keratinocyte migration. TAK1-deficient keratinocytes migrate faster, associated with enhanced integrin β1 and β5 expression, activation of FAK, and small Rho GTPases when compared with its wild-type counterpart. The elevated active Rho GTPases expression profile supports a faster migration rate and persistent lamellipodia formation. The functions of pVHL can be mediated via HIFα-dependent or -independent mechanisms. Our findings suggested that hypoxia retarded keratinocyte migration. However, hypoxia-mediated migration is complex and context-dependent. It can be modulated by extracellular matrix, matricellular proteins, matrix metalloproteinases, and other signaling pathways (33.O'Toole E.A. van Koningsveld R. Chen M. Woodley D.T. J. Cell. Physiol. 2008; 214: 47-55Crossref PubMed Scopus (32) Google Scholar). It can also differ among keratinocytes isolated from donors of different age (34.Xia Y.P. Zhao Y. Tyrone J.W. Chen A. Mustoe T.A. J. Invest. Dermatol. 2001; 116: 50-56Abstract Full Text Full Text PDF PubMed Scopus (79) Google Scholar). However, our findings suggest that the mechanism underlying the phenotype of TAK1-deficient keratinocytes is HIFα-independent. Interestingly, TAK1 employs similar regulatory mechanism, i.e. via pVHL to modulate integrin β1 and β5 expression. In support of a role in cell migration for pVHL, it was reported that highly aggressive breast cancer expressed either no pVHL or low pVHL level (35.Zia M.K. Rmali K.A. Watkins G. Mansel R.E. Jiang W.G. Int. J. Mol. Med. 2007; 20: 605-611PubMed Google Scholar). High pVHL expression also resulted in a decrease of tubulin turnover indicating a role for pVHL in cellular processes such as migration, polarization, and cell-cell interactions (36.Lolkema M.P. Mehra N. Jorna A.S. van Beest M. Giles R.H. Voest E.E. Exp. Cell Res. 2004; 301: 139-146Crossref PubMed Scopus (47) Google Scholar).The development, maintenance, and regeneration of the epidermal integrity are likely to involve the concerted effort of numerous signaling pathways, including epithelial-mesenchymal communications. One of such communications is the IL-1/keratinocyte growth factor/granulocyte macrophage-colony stimulating factor double paracrine mechanism (37.Maas-Szabowski N. Shimotoyodome A. Fusenig N.E. J. Cell Sci. 1999; 112: 1843-1853Crossref PubMed Google Scholar). Given the pivotal role of TAK1 in propagating the effect of numerous inflammatory cytokines, such as TNF-α, the PDGF/HGF mechanism described herein complements the IL-1/keratinocyte growth factor/granulocyte macrophage-colony stimulating factor mechanism, particularly during wound repair. TAK1 may also modulate cell migration indirectly via HGF in vivo, when epithelia-mesenchymal interaction is evident. It was recently shown that HGF-mediated cell migration involves a PAK-LIMK pathway (38.Ahmed T. Shea K. Masters J.R. Jones G.E. Wells C.M. Cell Signal. 2008; 20: 1320-1328Crossref PubMed Scopus (106) Google Scholar). It is conceivable that both mechanisms are utilized for epidermal regeneration during wound healing.Psoriasis is a non-contagious chronic inflammatory skin disease characterized by hyperproliferative epidermal growth, a phenotype that was similarly observed in mice with a keratinocyte-specific deletion of TAK1 (10.Omori E. Matsumoto K. Sanjo H. Sato S. Akira S. Smart R.C. Ninomiya-Tsuji J. J. Biol. Chem. 2006; 281: 19610-19617Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar, 11.Sayama K. Hanakawa Y. Nagai H. Shirakata Y. Dai X. Hirakawa S. Tokumaru S. Tohyama M. Yang L. Sato S. Shizuo A. Hashimoto K. J. Biol. Chem. 2006; 281: 22013-22020Abstract Full Text Full Text PDF PubMed Scopus (49) Google Scholar). A recent report suggests that TAK1 deletion causes dysregulation of reactive oxygen species in keratinocytes, which is causally associated with skin inflammation (39.Omori E. Morioka S. Matsumoto K. Ninomiya-Tsuji J. J. Biol. Chem. 2008; 283: 26161-26168Abstract Full Text Full Text PDF PubMed Scopus (78) Google Scholar). Reactive oxygen species has been associated with psoriasis (40.Trouba K.J. Hamadeh H.K. Amin R.P. Germolec D.R. Antioxid. Redox. Signal. 2002; 4: 665-673Crossref PubMed Scopus (215) Google Scholar, 41.Young C.N. Koepke J.I. Terlecky L.J. Borkin M.S. Boyd S.L. Terlecky S.R. J. Invest. Dermatol. 2008; 128: 2606-2614Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar). Our study reveals the underlying mechanism by which TAK1 regulates epidermal proliferation via a double paracrine mechanism involving the underlying dermal fibroblasts. We showed that TAK1 in the keratinocytes directly up-regulated the expression of pVHL, reduced PDGF-B expression, and consequently diminished HGF/c-Met signaling. A deficiency in TAK1 resulted in reduced NF-κB activation and pVHL expression. Lending support, analysis of skin biopsies of patients with psoriasis showed that pVHL, a direct target of TAK1, is underexpressed in psoriatic skin and highly expressed in healthy skin (42.Tovar-Castillo L.E. Cancino-Díaz J.C. García-Vázquez F. Cancino-Gómez F.G. León-Dorantes G. Blancas-González F. Jiménez-Zamudio L. García-Latorre E. Cancino-Díaz M.E. Int. J. Dermatol. 2007; 46: 239-246Crossref PubMed Scopus (83) Google Scholar). Furthermore, PDGF receptor expression was greatly elevated in psoriatic fibroblasts, rendering them highly responsive to PDGF and PDGF-induced HGF production (27.Krueger J.G. Krane J.F. Carter D.M. Gottlieb A.B. J. Invest. Dermatol. 1990; 94: 135S-140SAbstract Full Text PDF PubMed Scopus (203) Google Scholar). Altogether, our findings herein and those of others suggest that TAK1 deficiency may contribute to the etiology of psoriasis. Following injury, the restoration of its functional integrity is of utmost importance to the survival of the organism. The regeneration and maintenance of epithelium to close the wound is dictated by epithelial-mesenchymal interactions and purportedly mediated by the action of central players, such as chemokines and growth factors. This communication is crucial for preventing either insufficient or excess wound repair. Previous work has shown that mice with a keratinocyte-specific deletion of TAK1 exhibit severe skin inflammation and display abnormal epidermis with impaired differentiation, increased cell proliferation, and apoptosis (10.Omori E. Matsumoto K. Sanjo H. Sato S. Akira S. Smart R.C. Ninomiya-Tsuji J. J. Biol. Chem. 2006; 281: 19610-19617Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar, 11.Sayama K. Hanakawa Y. Nagai H. Shirakata Y. Dai X. Hirakawa S. Tokumaru S. Tohyama M. Yang L. Sato S. Shizuo A. Hashimoto K. J. Biol. Chem. 2006; 281: 22013-22020Abstract Full Text Full Text PDF PubMed Scopus (49) Google Scholar). In this study, we reveal that keratinocyte-specific TAK1 regulates epidermal proliferation via a double paracrine mechanism and characterize a novel unsuspected role of TAK1 in cell migration. We show that pVHL, whose expression is up-regulated by TAK1/IKK/NF-κB signaling, interacts and sequesters transcription factor Sp1, which is necessary for PDGF-B and integrins β1 and β5 expression. The formation of normal epidermal tissue requires a continuous exchange of signals with the underlying dermal fibroblasts (15.Chong H.C. Tan M.J. Philippe V. Tan S.H. Tan C.K. Ku C.W. Goh Y.Y. Wahli W. Michalik L. Tan N.S. J. Cell Biol. 2009; 184: 817-831Crossref PubMed Scopus (80) Google Scholar, 28.Cheng N. Bhowmick N.A. Chytil A. Gorksa A.E. Brown K.A. Muraoka R. Arteaga C.L. Neilson E.G. Hayward S.W. Moses H.L. Oncogene. 2005; 24: 5053-5068Crossref PubMed Scopus (223) Google Scholar). Keratinocyte-specific TAK1-knock-out mice displayed enhanced epidermal proliferation, which was not observed in monolayer culture, suggesting that dermal fibroblasts have pivotal contribution. We reveal a double paracrine PDGF/HGF signaling that plays an important role in TAK1-mediated epidermal proliferation. For any cells to respond productively to PDGF, they must possess corresponding cell surface receptors, either the α-PDGF or β-PDGF receptors. Although keratinocytes contribute to PDGF activity by their ample capacity to secreted PDGF, they do not express any transmembrane receptor recognizing any classic PDGF isoforms; thus target cells for these ligands in skin are restricted to cells of mesenchymal origin, e.g. dermal fibroblasts (29.Reuterdahl C. Sundberg C. Rubin K. Funa K. Gerdin B. J. Clin. Invest. 1993; 91: 2065-2075Crossref PubMed Scopus (100) Google Scholar, 30.Ansel J.C. Tiesman J.P. Olerud J.E. Krueger J.G. Krane J.F. Tara D.C. Shipley G.D. Gilbertson D. Usui M.L. Hart C.E. J. Clin. Invest. 1993; 92: 671-678Crossref PubMed Scopus (124) Google Scholar). We further show that NF-κB, a downstream mediator of TAK1, regulates the expression of pVHL. The pVHL protein interacts and sequesters transcription factor Sp1, which is required for PDGF-B expression (21.Rafty L.A. Khachigian L.M. J. Cell. Biochem. 2002; 85: 490-495Crossref PubMed Scopus (17) Google Scholar). A similar mechanism was also exploited by pVHL to repress VEGF gene expression (31.Mukhopadhyay D. Knebelmann B. Cohen H.T. Ananth S. Sukhatme V.P. Mol. Cell. Biol. 1997; 17: 5629-5639Crossref PubMed Scopus (304) Google Scholar). PDGF-B was previously reported to increase HGF production in the fibroblasts to stimulate keratinocyte proliferation (32.Lederle W. Stark H.J. Skobe M. Fusenig N.E. Mueller M.M. Am. J. Pathol. 2006; 169: 1767-1783Abstract Full Text Full Text PDF PubMed Scopus (51) Google Scholar). Indeed, PDGF-BB secreted by keratinocytes acts as a paracrine factor to induce HGF production by fibroblasts, which in return, enhance epidermal proliferation (Fig. 6). This study underscores the fact that TAK1 in the epidermal keratinocytes fulfils a homeostatic role during epidermal formation, modulating cell proliferation via a double paracrine fashion, involving the underlying dermal fibroblasts. The paracrine mechanism described herein emphasizes the importance of epithelial-mesenchymal communication in the regulation of epidermal proliferation, which was not observed in TAK1-knock-out monolayer culture. Cell migration during re-epithelialization is equally crucial for efficient wound closure. In this study, we reveal a novel homeostatic role of TAK1 in the control of keratinocyte migration. TAK1-deficient keratinocytes migrate faster, associated with enhanced integrin β1 and β5 expression, activation of FAK, and small Rho GTPases when compared with its wild-type counterpart. The elevated active Rho GTPases expression profile supports a faster migration rate and persistent lamellipodia formation. The functions of pVHL can be mediated via HIFα-dependent or -independent mechanisms. Our findings suggested that hypoxia retarded keratinocyte migration. However, hypoxia-mediated migration is complex and context-dependent. It can be modulated by extracellular matrix, matricellular proteins, matrix metalloproteinases, and other signaling pathways (33.O'Toole E.A. van Koningsveld R. Chen M. Woodley D.T. J. Cell. Physiol. 2008; 214: 47-55Crossref PubMed Scopus (32) Google Scholar). It can also differ among keratinocytes isolated from donors of different age (34.Xia Y.P. Zhao Y. Tyrone J.W. Chen A. Mustoe T.A. J. Invest. Dermatol. 2001; 116: 50-56Abstract Full Text Full Text PDF PubMed Scopus (79) Google Scholar). However, our findings suggest that the mechanism underlying the phenotype of TAK1-deficient keratinocytes is HIFα-independent. Interestingly, TAK1 employs similar regulatory mechanism, i.e. via pVHL to modulate integrin β1 and β5 expression. In support of a role in cell migration for pVHL, it was reported that highly aggressive breast cancer expressed either no pVHL or low pVHL level (35.Zia M.K. Rmali K.A. Watkins G. Mansel R.E. Jiang W.G. Int. J. Mol. Med. 2007; 20: 605-611PubMed Google Scholar). High pVHL expression also resulted in a decrease of tubulin turnover indicating a role for pVHL in cellular processes such as migration, polarization, and cell-cell interactions (36.Lolkema M.P. Mehra N. Jorna A.S. van Beest M. Giles R.H. Voest E.E. Exp. Cell Res. 2004; 301: 139-146Crossref PubMed Scopus (47) Google Scholar). The development, maintenance, and regeneration of the epidermal integrity are likely to involve the concerted effort of numerous signaling pathways, including epithelial-mesenchymal communications. One of such communications is the IL-1/keratinocyte growth factor/granulocyte macrophage-colony stimulating factor double paracrine mechanism (37.Maas-Szabowski N. Shimotoyodome A. Fusenig N.E. J. Cell Sci. 1999; 112: 1843-1853Crossref PubMed Google Scholar). Given the pivotal role of TAK1 in propagating the effect of numerous inflammatory cytokines, such as TNF-α, the PDGF/HGF mechanism described herein complements the IL-1/keratinocyte growth factor/granulocyte macrophage-colony stimulating factor mechanism, particularly during wound repair. TAK1 may also modulate cell migration indirectly via HGF in vivo, when epithelia-mesenchymal interaction is evident. It was recently shown that HGF-mediated cell migration involves a PAK-LIMK pathway (38.Ahmed T. Shea K. Masters J.R. Jones G.E. Wells C.M. Cell Signal. 2008; 20: 1320-1328Crossref PubMed Scopus (106) Google Scholar). It is conceivable that both mechanisms are utilized for epidermal regeneration during wound healing. Psoriasis is a non-contagious chronic inflammatory skin disease characterized by hyperproliferative epidermal growth, a phenotype that was similarly observed in mice with a keratinocyte-specific deletion of TAK1 (10.Omori E. Matsumoto K. Sanjo H. Sato S. Akira S. Smart R.C. Ninomiya-Tsuji J. J. Biol. Chem. 2006; 281: 19610-19617Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar, 11.Sayama K. Hanakawa Y. Nagai H. Shirakata Y. Dai X. Hirakawa S. Tokumaru S. Tohyama M. Yang L. Sato S. Shizuo A. Hashimoto K. J. Biol. Chem. 2006; 281: 22013-22020Abstract Full Text Full Text PDF PubMed Scopus (49) Google Scholar). A recent report suggests that TAK1 deletion causes dysregulation of reactive oxygen species in keratinocytes, which is causally associated with skin inflammation (39.Omori E. Morioka S. Matsumoto K. Ninomiya-Tsuji J. J. Biol. Chem. 2008; 283: 26161-26168Abstract Full Text Full Text PDF PubMed Scopus (78) Google Scholar). Reactive oxygen species has been associated with psoriasis (40.Trouba K.J. Hamadeh H.K. Amin R.P. Germolec D.R. Antioxid. Redox. Signal. 2002; 4: 665-673Crossref PubMed Scopus (215) Google Scholar, 41.Young C.N. Koepke J.I. Terlecky L.J. Borkin M.S. Boyd S.L. Terlecky S.R. J. Invest. Dermatol. 2008; 128: 2606-2614Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar). Our study reveals the underlying mechanism by which TAK1 regulates epidermal proliferation via a double paracrine mechanism involving the underlying dermal fibroblasts. We showed that TAK1 in the keratinocytes directly up-regulated the expression of pVHL, reduced PDGF-B expression, and consequently diminished HGF/c-Met signaling. A deficiency in TAK1 resulted in reduced NF-κB activation and pVHL expression. Lending support, analysis of skin biopsies of patients with psoriasis showed that pVHL, a direct target of TAK1, is underexpressed in psoriatic skin and highly expressed in healthy skin (42.Tovar-Castillo L.E. Cancino-Díaz J.C. García-Vázquez F. Cancino-Gómez F.G. León-Dorantes G. Blancas-González F. Jiménez-Zamudio L. García-Latorre E. Cancino-Díaz M.E. Int. J. Dermatol. 2007; 46: 239-246Crossref PubMed Scopus (83) Google Scholar). Furthermore, PDGF receptor expression was greatly elevated in psoriatic fibroblasts, rendering them highly responsive to PDGF and PDGF-induced HGF production (27.Krueger J.G. Krane J.F. Carter D.M. Gottlieb A.B. J. Invest. Dermatol. 1990; 94: 135S-140SAbstract Full Text PDF PubMed Scopus (203) Google Scholar). Altogether, our findings herein and those of others suggest that TAK1 deficiency may contribute to the etiology of psoriasis. We thank Dr. Samuel Ko and Anna Teo (Carl Zeiss, Singapore Pte Ltd.) for their expertise in image acquisition using the MIRAX MIDI. Supplementary Material Download .pdf (1.25 MB) Help with pdf files Download .pdf (1.25 MB) Help with pdf files
Referência(s)